Image encoding/decoding method and apparatus using block transformation

ABSTRACT

Video encoding/decoding method and apparatus using a block transformation are disclosed. The apparatus encodes the video through predicting each pixel in a current block of the video by using one or more adjacent pixels, which are encoded prior to encoding the current block and have the closest proximity to the pixels respectively in a predetermined prediction direction, and wherein the current block is sized L×M with L being unequal to M. It has become possible to predict the pixels in the block starting from closest one of the pixels in the prediction direction in order to provide more accurate block predictions and then raise the compression efficiency that leaps to more efficient video encoding/decoding performance.

TECHNICAL FIELD

The present disclosure relates to a video encoding/decoding method andapparatus using a block transformation. More particularly, the presentinvention relates to a video encoding/decoding method for a currentblock through its prediction from the adjacent blocks whereinpredictions are performed on the entire pixels of the current blockstarting from closest one of the pixels in the prediction direction.

Background Art

Moving Picture Experts Group (MPEG) and Video Coding Experts Group(VCEG) have developed an improved and excellent video compressiontechnology over existing MPEG-4 Part 2 and H.263 standards. The newstandard is called H.264/AVC (Advanced Video Coding) and was releasedsimultaneously as MPEG-4 Part 10 AVC and ITU-T Recommendation H.264.Such H.264/AVC (hereinafter referred to as ‘H.264’) uses a spatialpredictive coding method, which is different from conventional videocoding international standards such as MPEG-1, MPEG-2, MPEG-4 Part2Visual and the like.

Conventional video coding methods use “intra prediction” forcoefficients transformed in Discrete Cosine Transform Domain (or DCTTransform Domain) to seek higher encoding efficiency resulting indegradation of the subjective video quality at low band transmission bitrates. However, H.264 adopts the method of encoding based on a spatialintra prediction in a spatial domain rather than in a transform domain.

An encoder that uses a coding method based on the conventional spatialintra prediction predicts current block information from information ofthe previously encoded and reconstructed previous blocks, encodesinformation on just the difference of the prediction block from theactual block to encode, and transmits the encoded information to adecoder. Then, the encoder may transmit parameters needed for predictionof the block to the decoder or the encoder and decoder may besynchronized, so that they share the needed parameters for the decoderto predict the block. In terms of the decoder, the block information tobe currently decoded is predicted using previously decoded andreconstructed adjacent block information and then added to thedifference information transmitted from the encoder, which reconstructsthe block to be decoded. Then, again, if the parameters needed for theprediction are transmitted from the decoder, the parameters can bedecoded and used for prediction.

The above described intra prediction may be an intra_(—)4×4 prediction,intra_(—)16×16 prediction, intra_(—)8×8 prediction and the like, wherethe respective intra predictions include a plurality of predictionmodes.

FIG. 1 is a diagram showing conventional nine 4×4 intra predictionmodes.

Referring to FIG. 1, the intra_(—)4×4 prediction has nine predictionmodes which include a vertical mode, horizontal mode, direct current(DC) mode, diagonal down-left mode, diagonal down-right mode,vertical-right mode, horizontal-down mode, vertical-left mode andhorizontal-up mode.

FIG. 2 is a diagram showing conventional four 16×16 intra predictionmodes.

In FIG. 2, the intra_(—)16×16 prediction has four prediction modes whichinclude a vertical mode, horizontal mode, DC mode and plane mode. Theintra_(—)8×8 prediction also has four modes similar to theintra_(—)16×16 prediction.

All of the intra prediction modes described in FIGS. 1 and 2 predict thecurrent blocks by generating predicted pixel values from the previouslyencoded or decoded pixels neighboring the current blocks. Typically inH.264, the intra predictions are performed in square block unit, and theprediction blocks for the intra prediction are sized 16×16, 8×8, and 4×4for the intra_(—)16×16 prediction, intra_(—)8×8 prediction, andintra_(—)4×4 prediction, respectively.

The reason for carrying out intra predictions in the N×N sized square isthat the subsequent discrete cosine transform (hereinafter called DCTtransform) for compressing the post-intra prediction residual signalsand the quantization procedure are likewise performed by regular square(4×4, 8×8). However, performing the intra predictions by such regularsquare blocks may degrade the accuracy of prediction since the pixels tobe predicted are predicted using relatively distant pixels, resulting inlow efficiency of the compression.

FIG. 3 illustrates adjacent pixels and the current block pixels used forthe typical intra_(—)16×16 prediction.

256 pixels in the lower case letters a₀ to p₁₅ represent the pixels inthe current block, while 32 pixels in the upper case A to AF areadjacent pixels of the neighboring blocks which had been compressedprior to the compression of the current block. For the vertical intraprediction in FIG. 3, the first column of pixels a₀˜a₁₅ may be predictedfrom pixel A, and the second column of pixels b₀˜b₁₅ may be predictedfrom pixel B. The remaining pixels c₀˜p₁₅ may be predicted from theupper pixels C-P, respectively. In this case, the pixels a₀˜p₀ arepredicted from the adjacent pixels A˜P with the spatially closestproximity in the direction of prediction, but the pixels a₁˜p₁ arespatially distanced from the adjacent pixels A˜P by two pixels as thepixels a₁₅˜p₁₅ are spatially distanced from the adjacent pixels A˜P bysixteen pixels, which degrades the accuracy of the intra prediction andin turn the compression efficiency.

DISCLOSURE Technical Problem

Therefore, the present disclosure has been made in view of the abovementioned problems to provide a video encoding/decoding of a currentblock through its prediction from the adjacent blocks wherein theprediction of the entire pixels of the current block is performedstarting from the most proximal pixel along the direction of predictionbefore the video encoding/decoding.

Technical Solution

One embodiment of the present disclosure provides an apparatus forencoding an input video comprising an intra predictor for predicting arectangular current block by using one or more adjacent pixels accordingto a predetermined prediction direction and generating a rectangularprediction block; a block rectangle-shaper for generating therectangular shape of the current block according to the predictiondirection from the input video; a subtractor for generating arectangular residual block by subtracting the rectangular predictionblock from the rectangular current block; a rearranger for rearrangingthe rectangular residual block into a square residual block; atransformer for transforming the square residual block into a frequencydomain; a quantizer for performing quantization with respect to thetransformed residual block; and an encoder for encoding the quantizedresidual block into a bitstream.

Another embodiment provides a method for encoding an input videocomprising: performing intra prediction for predicting a rectangularcurrent block by using one or more adjacent pixels according to apredetermined prediction direction and generating a rectangularprediction block; performing a rectangle-shaping with respect to a blockfor generating the rectangular shape of the current block from the inputvideo according to the prediction direction; subtracting the rectangularprediction block from the rectangular current block and generating arectangular residual block; rearranging the rectangular residual blockinto a square residual block; transforming the square residual blockinto a frequency domain; performing quantization with respect to thetransformed residual block; and encoding the quantized residual blockinto a bitstream.

Yet another embodiment provides apparatus for decoding a videocomprising: a decoder for decoding a bitstream and extracting residualblock; an inverse quantizer for performing an inverse quantization withrespect to the extracted residual block; an inverse transformer forperforming an inverse transformation with respect to the inversequantized residual block into a time domain; an inverse rearranger forperforming an inverse rearrangement with respect to the inversetransformed residual block into a rectangular residual block accordingto a predetermined prediction direction; an intra predictor forpredicting a rectangular current block by using one or more adjacentpixels according to the prediction direction and generating arectangular prediction block; an adder for adding the rectangularresidual block to the rectangular prediction block in order to generatethe rectangular current block; and a reconstructor for reconstructingthe video for output by using the rectangular current block according tothe prediction direction.

Yet another embodiment provides a method for decoding a videocomprising: decoding a bitstream and extracting residual block;performing an inverse quantization with respect to the extractedresidual block; performing an inverse transformation with respect to theinverse quantized residual block into a time domain; performing aninverse rearrangement with respect to the inverse transformed residualblock into a rectangular residual block according to a predeterminedprediction direction; performing an intra prediction with respect to arectangular current block by using one or more adjacent pixels accordingto the prediction direction and generating a rectangular predictionblock; adding the rectangular residual block to the rectangularprediction block in order to generate the rectangular current block; andreconstructing the video for output by using the rectangular currentblock according to the prediction direction.

Yet another embodiment provides an apparatus for encoding a video havinga current block with pixels by using one or more respectively adjacentpixels encoded prior to encoding the current block and each having thehighest proximity to the respective current block pixels in apredetermined prediction direction, wherein the current block being ablock sized L×M with L being unequal to M.

Yet another embodiment provides an apparatus for decoding a video havinga current block with pixels by using one or more respectively adjacentpixels encoded prior to decoding the current block and each having thehighest proximity to the respective current block pixels in apredetermined prediction direction, wherein the current block being ablock sized L×M with L being unequal to M.

Advantageous Effects

As described above, according to the disclosure, the current block of avideo is predicted from the adjacent blocks for encoding/decoding thevideo wherein the prediction of the pixels in the block can be performedstarting from the adjacent pixels with the highest proximity in thespatial prediction direction, thereby improving the accuracy of theblock predictions toward a better compression efficiency to achieve anefficient encoding/decoding of the video.

DESCRIPTION OF DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a diagram showing conventional nine 4×4 intra predictionmodes;

FIG. 2 is a diagram showing conventional four 16×16 intra predictionmodes;

FIG. 3 illustrates adjacent pixels and the current block pixels used forthe typical intra_(—)16×16 prediction;

FIG. 4 is a schematic block diagram of an electronic configuration of avideo encoding apparatus according to an embodiment;

FIG. 5 is a flow diagram for illustrating a method for encoding a videoaccording to an embodiment;

FIG. 6 is a schematic block diagram of an electronic configuration of avideo decoding apparatus according to an embodiment;

FIG. 7 is a flow diagram for illustrating a method for decoding a videoaccording to an embodiment;

FIG. 8 is a diagram for illustrating a rectangular current block for theintra_(—)16×16 prediction according to an embodiment;

FIG. 9 is a diagram for illustrating a rearrangement of a 16×1 ofrectangular residual block into a square residual block according to anembodiment;

FIG. 10 is a diagram showing a rectangular current block for theintra_(—)8×8 prediction according to an embodiment;

FIG. 11 is a diagram for illustrating a rearrangement of an 8×2 ofrectangular residual block into a square residual block according to anembodiment; and

FIG. 12 at a and b illustrates the Rate-Distortion curves according tothe conventional and presently disclosed methods, respectively.

MODE FOR INVENTION

FIG. 4 is a schematic block diagram of an electronic configuration of avideo encoding apparatus according to an embodiment.

A video encoding apparatus 400 according to an embodiment of the presentdisclosure is configured to encode a video having a current block withpixels by using one or more respectively adjacent pixels encoded priorto encoding the current block pixels and each having the highestproximity to the respective current pixels in a predetermined predictiondirection, and the encoding apparatus 400 may be comprised of a blockrectangle-shaper 410, an intra predictor 420, a subtractor 430, arearranger 440, a transformer 450, a quantizer 460, and an encoder 470.Here, the current block may be a block sized L×M with L being unequal toM.

Video encoder 400 may be a personal computer or PC, notebook or laptopcomputer, personal digital assistant or PDA, portable multimedia playeror PMP, PlayStation Portable or PSP, or mobile communication terminal orsuch devices, and may represent a variety of apparatuses equipped with,for example, a communication system such as a modem for carrying outcommunications between various devices or wired/wireless communicationnetworks, a memory for storing various programs for encoding videos andrelated data, and a microprocessor for executing the programs to effectoperations and controls.

From an input video, block rectangle-shaper 410 generates a rectangularcurrent block according to a prediction direction.

Here, the prediction direction refers to such prediction directions asdetermined by various intra prediction modes (i.e., the respective fourprediction modes in the intra_(—)8×8 prediction and in theintra_(—)16×16 prediction) from which intra predictor 420 selects thefitting prediction direction to the characteristics of the video,thereby electing its optimal prediction mode. Therefore, upon receivinginformation on the prediction direction from intra predictor 420, blockrectangle-shaper 410 may generate the rectangular current block in thatprediction direction.

The rectangular current block means a current block to be encoded thatis configured in a rectangular shape. Specifically, because a typicalencoding scheme performs discrete cosine transform by blocks of 4×4 orsuch N×N size and then enters quantization, it is also preferable tohave the current block configured as an N×N sized square when predictingthe values of pixels in the current block. In this occasion, however,the prediction of the current block pixels needs to use the adjacentpixels with farther distances from the current pixel to predictdepending on the prediction direction, causing low efficiency of theprediction. To solve this problem, the present disclosure adopts currentblock rectangles of size 16×1, 1×16, 8×2, 2×8 or so as L×M (where L≠M)in order to employ the adjacent pixels with the highest proximity inpredicting the current pixel values to thereby improve the predictionefficiency. The thus predicted current block or rectangular predictionblock in L×M sized rectangle is subtracted by the rectangular currentblock that has been transformed from the input video in blockrectangle-shaper 410 to generate a rectangular residual block, which isrearranged by rearranger 440 into an N×N square residual block before itcan be transformed into a frequency domain by utilizing transformer 450that performs DCT transform in N×N size of block unit.

In generating the rectangular current block in the prediction directionfrom the input video as described above, if an intra block is defined asa 16×16 block and the prediction direction is vertical, then the blockrectangle-shaper 410 may either derive a 16×1 sized block rectangle (rowform) from the input video to allow each of the current block pixels tobe predicted from the adjacent pixels with the vertically closestproximity or derive a 1×16 sized block rectangle (column form) from theinput video to allow each of the current block pixels to be predictedfrom the adjacent pixels with the horizontally closest proximity.

If an intra block is defined as a 8×8 block and the prediction directionis vertical, then block rectangle-shaper 410 may derive a 8×2 sizedblock rectangle (2-row form) from the input video to allow each of thecurrent block pixels to be predicted from the adjacent pixels with thevertically closest proximity, and if an 8×8 block is defined and theprediction direction is horizontal, then it may derive a 2×8 sized blockrectangle (2-column form) from the input video to allow each of thecurrent block pixels to be predicted from the adjacent pixels with thehorizontally closest proximity. Here, to have the block sized 2×8 or 8×2and shaped in “2 columns” for the intra block of 8×8 shape is intendedto make the total pixel number of 16, which can be rearranged squarelyinto N×N sizes such as 4×4 so that transformer 450 and quantizer 460 maytransform and quantize the same in N×N sizes of the block.

In short, the presently disclosed rectangular block such as therectangular current block, rectangular prediction block, or rectangularresidual block may be an L×M sized block with L and M being unequal asdetermined in accordance with the above described prediction direction.In particular, if the prediction direction is vertical, L may be greaterthan M as in 16×1 and 8×2, and if the prediction direction ishorizontal, L may be less than M as in 1×16 and 2×8.

Intra predictor 420 may predict the rectangular current block by usingone or more adjacent pixels in a predetermined direction to generate arectangular prediction block. Herein, intra predictor 420 may find theprediction direction by performing predictions with respect to apredetermined size of intra block in different prediction modes anddetermining a lowest-cost prediction mode as the optimal predictionmode, although the predictions may be made alternatively in acquiredprediction directions upon acquiring information on such directions.Herein, intra predictor 420 may find the prediction direction byperforming predictions with respect to a predetermined size of intrablock in different prediction modes and determining a lowest-costprediction mode as the optimal prediction mode, although the predictionsmay be made alternatively in acquired prediction directions uponacquiring information on such directions. In such a case, the abovedescribed block rectangle-shaper 410 may also acquire information on thepredetermined prediction direction from other source than intrapredictor 410.

Intra predictor 420 knowing the prediction direction may predict each ofthe current block pixels by using one or more pixels, which werepreviously encoded before the encoding of the currently selected currentblock and are in proximity to the current block in the predictiondirection. In other words, in a similar manner to block rectangle shaper410, intra predictor 420 may select the rectangular current block pixelsto be predicted and predict them by using one or more pixels containedin the rectangular adjacent block that is selected from the adjacentrectangular blocks encoded previously of the rectangular current blockas being in a close proximity to the rectangular current block in theprediction direction.

Herein, being in proximity in the prediction direction means that if therectangular current block is in a row form, the row of pixels isaccompanied above and below thereof by two blocks with a close proximityto the current block where the pixels in the previously encoded one ofthe two blocks become the adjacent pixels. Being in proximity in theprediction direction also means that if the rectangular current block isin a column form, the column of pixels is accompanied left and rightthereof by two blocks with a close proximity to the current block wherethe pixels in the previously encoded one of the two blocks become theadjacent pixels.

Subtractor 430 may subtract the rectangular prediction block from therectangular current block to generate a rectangular residual block.Therefore, subtractor 430 may subtract the predicted pixel value of eachof the pixels in the rectangular prediction block supplied by intrapredictor 420 from the original pixel value of each of the pixels in therectangular current block supplied by block rectangle-shaper 410 togenerate the residual signal between the pixels in the shape of arectangular residual block.

Rearranger 440 may rearrange the rectangular residual block into asquare residual block. That is, rearranger 440 may rearrange therectangular residual block generated by subtractor 430 into the squareform so that it can be immediately used in DCT transform by transformer450, which operates on N×N sized square blocks. The operation ofrearranger 440 to turn the rectangular residual block into its squareequivalent will be described in detail below with reference to FIGS. 8to 11.

Transformer 450 may transform the square residual block into frequencydomain. In transforming the rectangular residual block to the frequencydomain, transformer 450 may use the DCT transform, although it is not solimited that various other improved or modified transformationtechniques may be used with or without involving the DCT fortransforming the video signal of time-domain into that of frequencydomain.

Quantizer 460 may quantize the transformed residual block fromtransformer 450. According to an embodiment, while the rectangularcurrent block is to predict through using the previously encodedadjacent pixels in order to predict each of the pixels in the currentblock from the highest proximal pixel, the transformer 450 and quantizer460 may operate by unit of 16 pixels (4×4 pixels) to carry out thetransform into the frequency domain and quantization as in the typicaltransform in H.264. This became possible with rearranger 440transforming the rectangular residual block into the square residualblock that is properly squared as N×N to be processed in transformer 450and quantizer 460.

The encoder 470 encodes the quantized residual block into bitstream.

Encoder 470 may encode information on prediction modes and predictiondirections determined in intra predictor 420 along with the quantizedresidual block. Entropy encoding may be used for the encodingtechnology, although it is not to limit employing various other encodingmethods.

FIG. 5 is a flow diagram for illustrating a method for encoding a videoaccording to an embodiment.

In operation, video encoding apparatus 400 reduces data amount toachieve a higher encoding efficiency by encoding the difference betweenthe values of the actual pixels in the current block to be encoded andthe values of the pixels in the predicted current block from theadjacent previously encoded blocks, in other words, by encoding theresidual signal.

In order to obtain predicted pixel values of the current block in a wayto improve both the accuracy of prediction and the efficiency ofcompression through having the pixels be predicted from the mostproximal pixels, video encoding apparatus 400 may predict a rectangularcurrent block by using one or more adjacent pixels in a predeterminedprediction direction and generate a rectangular prediction block in stepS510, and it may generate the rectangular current block according to theprediction direction from an input video at S530.

With the rectangular prediction block and rectangular current blockgenerated, video encoding apparatus 400 subtracts the rectangularprediction block from the rectangular current block to generate arectangular residual block at S535, and rearranges the rectangularresidual block into a square residual block at S540.

Upon rearranging the residual block into a square, video encodingapparatus 400 transforms the squared residual block into a frequencydomain through DCT transform or similar process at S550, performsquantization with respect to the transformed square residual block atS560, and encodes the quantized square residual block into bitstream atS570. When encoding the quantized residual block into bitstream, videoencoding apparatus 400 may also encode information on the predictiondirection in accordance with the prediction mode along with the residualblock into bitstream.

The encoded bitstream of video by the video encoding apparatus 400 asdescribed above may then be transmitted in real time or non-real-time tovideo decoding apparatuses for decoding the same before itsreconstructions and reproductions via a wired/wireless communicationnetwork including the Internet, a short range wireless communicationnetwork, a wireless LAN network, WiBro (Wireless Broadband) also knownas WiMax network, and mobile communication network or a communicationinterface such as cable or USB (universal serial bus).

FIG. 6 is a schematic block diagram of an electronic configuration of avideo decoding apparatus according to an embodiment.

A video decoding apparatus 600 according to an embodiment of the presentdisclosure is adapted to decode a video having a current block withpixels by using one or more respectively adjacent pixels encoded priorto decoding the current block pixels and each having the highestproximity to the respective current pixels in a predetermined predictiondirection, and the video decoding apparatus 600 may be comprised of adecoder 610, an inverse quantizer 620, an inverse transformer 630, aninverse rearranger 640, an adder 650, an intra predictor 660, and arectangular block reconstructor 670. Here, the current block may be ablock sized L×M where L unequals to M.

As described for the video encoding apparatus 400 with reference to FIG.4, the video decoder 600 may be a personal computer or PC, personaldigital assistant or PDA, portable multimedia player or PMP, PlayStationPortable or PSP, or mobile communication terminal or such devices, andmay represent a variety of apparatuses equipped with, for example, acommunication system such as a modem for carrying out communicationsbetween various devices or wired/wireless communication networks, amemory for storing various programs for encoding videos and relateddata, and a microprocessor for executing the programs to effectoperations and controls.

Decoder 610 may decode bitstream to extract a square residual block. Tobe specific, decoder 610 decodes the bitstream of the encoded video byvideo encoding apparatus 400 to extract the square residual block, whichincludes pixel information of the current block of the video.

When decoding the bitstream to extract the residual block from thebitstream of the encoded video received from video encoding apparatus400, decoder 610 may further extract information on the prediction modeor on the prediction direction if it is included in the bitstream forperforming the intra prediction. Therefore, video encoding apparatus 400and video decoding apparatus 600 may be synchronized to operate withrespect to the prediction direction for the intra prediction so that theintra prediction is consistently performed in a predetermined directionof prediction and alternatively the video encoding apparatus 400 maytake its video encoding session to further encode the information on theprediction direction for the intra prediction into the bitstream andthen the video decoding apparatus 600 in its decoding session may alsoextract the information on the prediction direction from the bitstreamin order to know the direction of prediction.

Inverse quantizer 620 may perform inverse quantization orde-quantization with respect to the square residual block extracted bydecoder 610 from the bitstream. Inverse transformer 630 may performinverse transformation with respect to the inverse quantized squareresidual block by inverse quantizer 620 into time domain.

Inverse rearranger 640 may rearrange the inverse transformed squareresidual block by inverse transformer 630 back into the rectangularresidual block in line with the prediction direction. Particularly, uponreceiving the inverse transformed square residual block from inversetransformer 630, inverse rearranger 640 checks the prediction directionto determine the size of the required block rectangle in which thesquare residual block should be transformed in line with the predictiondirection. For example, in the case of vertical prediction direction,the rectangular block sized L×M may be so determined as to be L>M like16×1 or 8×2, and in the horizontal prediction direction it may be setL<M as in 1×16 or 2×8.

If it is set as L>M for the vertical prediction direction, whether tomake the inverse rearrangement into a 16×1 sized rectangular residualblock or a 8×2 sized such block may then be determined by theinformation synchronized between video encoding apparatus 400 and videodecoding apparatus 600, and the same applies to whether to make theinverse rearrangement into a 1×16 sized rectangular residual block or a2×8 sized block if L<M for the horizontal prediction direction. In otherwords, if the synchronization between video encoding apparatus 400 andvideo decoding apparatus 600 is set to perform the intra 16×16prediction with respect to the current block or the current frame, theinverse rearrangement may be performed toward 16×1 (for verticaldirection) or 1×16 (horizontal direction) sized rectangular residualblock, and if the synchronization therebetween is set to perform theintra 8×8 prediction with respect to the current block or the currentframe, the inverse rearrangement may be performed toward 8×2 (forvertical direction) or 2×8 (horizontal direction) sized rectangularresidual block.

In addition, the prediction direction may be determined by using theinformation extracted from the bitstream at decoder 610, or it maycorrespond to the synchronized prediction direction or prediction modebetween video decoding apparatus 600 and video encoding apparatus 400while inverse rearranger 640 may acquire such information on theprediction direction either from decoder 610 or from other sources thatstores it.

Adder 650 may add the rectangular residual block generated in inverserearranger 640 to the rectangular prediction block from intra predictor660 in order to generate the rectangular current block.

Intra predictor 660 may predict the rectangular current block by usingone or more adjacent pixels in the prediction direction to generate therectangular prediction block. That is, intra predictor 660 may acquireeither the information on the extracted prediction direction from thebitstream in decoder 610 or the prediction directional portion of theentire information in synchronization with video encoding apparatus 400to get the prediction direction and accordingly identify the size andshape of the current block (i.e., any size and shape out of 16×1, 1×16,8×2, or 2×8) in order to predict the identified current block pixels oneby one using one or more adjacent pixel values in the predictiondirection. Here, one or more adjacent pixels refer to those decodedprior to decoding the identified rectangular current block as describedabove and being adjacent to the same block along the predictiondirection.

Rectangular block reconstructor 670 may reconstruct the output video byusing the rectangular current block along the described predictiondirection as described above. More specifically, since the current blockoutput from adder 650 has been shaped into the rectangle by adding theinverse rearranged rectangular residual block to the prediction block inintra predictor 660, it is in condition for adding in the predictiondirection to the previously decoded rectangular block that underwent thedecoding process immediately before decoding this current blockfollowing the prediction direction in order to reconstruct the outputvideo. For example, if the prediction direction is vertical, thepreviously decoded rectangular block that underwent the decoding processjust before decoding this current block and the current block are bothin row form of rectangles and sized 16×1 or 8×2 and thus the presentlydecoded current block may be added as a lower row to the previouslydecoded rectangular block, thereby reconstructing the output video.

FIG. 7 is a flow diagram for illustrating a method for decoding a videoaccording to an embodiment.

Upon receiving bitstream for the video via a wired/wirelesscommunication network or cable, video decoding apparatus 600 may storethe same before reproducing the video through decoding andreconstructing following an algorithm of the user's choice of a programor another program in execution.

To this end, video decoding apparatus 600 may decode the bitstream toextract a square residual block representing information on the currentblock of the video at S710. Video decoding apparatus 600 may performinverse quantization with respect to the extracted square residual blockat S720, perform inverse transformation with respect to the inversequantized square residual block into a time domain at S730, and performinverse rearrangement with respect to the inverse transformed residualblock of the time domain into a rectangular residual block in thepredicted direction at S740.

Video decoding apparatus 600 may predict a rectangular current block byusing one or more adjacent pixels in their prediction directions togenerate a rectangular prediction block at S750, add the rectangularresidual block to the rectangular prediction block to generate therectangular current block at S760, and reconstruct the video by usingthe rectangular current block according to the prediction direction atS770.

FIG. 8 is a diagram showing a rectangular current block for theintra_(—)16×16 prediction according to an embodiment.

Upon receiving the input video, block rectangle-shaper 410 of videoencoding apparatus 400 may acquire the prediction direction that ispredetermined or determined by intra predictor 420 to generate therectangular current block along the prediction direction from the inputvideo. In addition, rectangular block reconstructor 670 may reconstructthe output video in the prediction direction by using the rectangularcurrent block. FIG. 8 shows the rectangular current block in 16×16prediction with the prediction direction being vertical.

The respective pixels marked by upper case A˜P are adjacent pixels thathave been encoded or decoded previously, as the lower case a_(x)˜p_(x)(x=0, 1, 2, . . . , 15) indicate the respective macroblock pixels sized16×16. In the typical intra 16×16 prediction, if the prediction is invertical direction, a₁ may be predicted from the adjacent pixel A withthe closest proximity but a₁₅ have to be predicted from the fairlyremote adjacent pixel A. Therefore, the predicted pixel value of a₁₅should have low prediction accuracy.

However, in the present disclosure, intra predictor 420 of videoencoding apparatus 400 as well as intra predictor 660 of video decodingapparatus 600 may predict a 16×1 rectangular current block 810 withpixels a_(x)˜p_(x) (x=0, 1, 2, . . . , 15) rather than 16×16 sized blockby using the adjacent block 820 that was previously encoded or decodedand has pixels A˜P with the respectively closest proximity to the pixelsof current block 810.

FIG. 9 is a diagram for illustrating a rearrangement of a 16×1 ofrectangular residual block into a square residual block.

Predicting the respective values of the pixels a₀˜p₀ of the rectangularcurrent block 810 shown in FIG. 8 with the respective values of thepixels A˜P of the adjacent encoded block 820 may yield the rectangularresidual block 910 as shown in FIG. 9 (r₀=original pixel value ofa₀—predicted pixel value of a₀).

When the rectangular residual block 910 is generated as shown in FIG. 9,rearranger 440 may rearrange the 16×1 sized residual block 910 into a4×4 sized square residual block 920. Here, the 16×1 sized residual block910 may be classified into four 4×1 sized rectangular residual blocks(912 to 918), as rearranger 440 arranges the four blocks (912 to 918)respectively to different rows within the 4×4 sized square residualblock 920 generated.

Specifically, in the rectangular residual block 910, the first residualblock 912 forms the first row of the square residual block 920, andlikewise, the second residual block 914 the second row, the thirdresidual block 916 the third row, and the fourth residual block 918 thefourth row thereof.

The rearranged square residual block 920 by the rearranger 440 asdescribed above may be transformed by the transformer 450 into thefrequency domain and quantized by quantizer 460 before being encodedinto a bitstream by encoder 470.

In the video decoding apparatus 600, decoder 610 may extract a squareresidual block from the bitstream received from the video encodingapparatus 400, perform inverse quantization with respect to the squareresidual block at the inverse quantizer 620, perform inverse transformwith respect to the square residual block at inverse transformer 630 andthen perform inverse rearrangement with respective to the squareresidual block into rectangular residual block.

In other words, inverse rearranger 640 rearranges the square residualblock 920 illustrated in FIG. 9 back into the rectangular residual block910 in a reverse process to reconstruct the first row of the squareresidual block 920 into the first residual block 912 of the rectangularresidual block 910, the second row of the square residual block 920 intothe second residual block 914 of the rectangular residual block 910, thethird row of the square residual block 920 into the third residual block916 of the rectangular residual block 910, and the fourth row of thesquare residual block 920 into the fourth residual block 918 of therectangular residual block 910.

When the rectangular residual block 910 is reconstructed by the inverserearranger 640, intra predictor 660 of video decoding apparatus 600identifies the rectangular current block that corresponds to thereconstructed rectangular residual block 910, predicts the value of eachpixel in the identified rectangular current block by using the adjacentpixels A˜P which were previously decoded and are in proximity with thecurrent block in the prediction direction that is vertical in thisexemplary description, and then adder 650 adds the rectangularprediction block to the rectangular residual block to generate therectangular current block 810.

In this way, from the encoded or decoded rectangular current block, i.e.the 16×16 block for the intra 16×16 prediction at its first row pixelsa₀˜p₀, the prediction is performed with respect to the second row pixelsa₁˜p₁ by using the reconstructed pixels a₀˜p₀ as the predictors thereforin order to encode or decode the same. Likewise, the third row pixelsmay be predicted from the second row pixels. The same process may beapplied to all the rows enabling the entire pixels in the macroblockunder the intra 16×16 prediction to be predicted starting from theadjacent pixel with the closest proximity in the prediction directionbefore being compressed/reconstructed.

Similar to the vertical prediction direction, pixel predictions in thehorizontal direction may be performed for the entire pixels startingfrom the most proximal adjacent pixel for theircompression/reconstruction.

On the other hand, although the above description is directed to theintra_(—)16×16 prediction with FIGS. 8 and 9, the present disclosure mayalso apply to the intra 8×8 prediction.

FIG. 10 is a diagram showing a rectangular current block for theintra_(—)8×8 prediction according to an embodiment.

In FIG. 8, illustrated was the intra_(—)8×8 prediction for therectangular current block with the prediction direction set to behorizontal.

The respective pixels marked by upper cases A˜H are adjacent pixels thathave been encoded or decoded previously, as the lower cases a₀˜h₇indicate the respective macroblock pixels sized 8×8 in the intraprediction. In the typical intra_(—)8×8 prediction, assuming theprediction is in vertical direction, a₀ may be predicted from adjacentpixel A with the closest proximity but a₇ has to be predicted fromadjacent pixel A from a fairly extended distance. Therefore, thepredicted pixel value of a₁₅ has a low accuracy.

In an embodiment of the present disclosure, intra predictor 420 of videoencoding apparatus 400 as well as intra predictor 660 of video decodingapparatus 600 may predict an 8×2 sized rectangular current block 1010with pixels a₀˜h₁ instead of the 8×8 sized block by using the adjacentblock 1020 that was previously encoded or decoded and has pixels A˜Hwith the respectively closest proximity to the pixels of current block1010.

When predicting the rectangular current block 1010, its first row andsecond row pixels a₀˜h₀ and a₁˜h₁ may be respectively predicted from thepixels A˜H, thereby determining the predicted pixel values. Subtractingthe predicted pixel value of each pixel in the rectangular current block1010 from the original pixel value of each pixel in the same currentblock 1010 may yield a rectangular residual block as shown in FIG. 11.

FIG. 11 is a diagram for illustrating a rearrangement of an 8×2 ofrectangular residual block into a square residual block according to anembodiment.

Upon generating the rectangular residual block 1110, rearranger 440 mayrearrange the 8×2 sized rectangular residual block 1110 into a 4×4 sizedsquare residual block 1120. Here, the 8×2 sized residual block 1110 canbe divided into four 4×1 sized rectangular residual blocks (1112 to1118), as rearranger 440 arranges the four blocks (1112 to 1118)respectively to different rows within the 4×4 sized square residualblock 1120.

Specifically, in the rectangular residual block 1110, the first residualblocks 1112 forms the first row of the square residual block 1120, thesecond residual block 1114 the second row, the third residual block 1116the third row, and the fourth residual block 1118 the fourth rowthereof.

The rearranged square residual block 1120 as described above may betransformed by the transformer 450 into the frequency domain andquantized by quantizer 460 prior to being encoded into a bitstream byencoder 470.

In the video decoding apparatus 600, decoder 610 may extract a squareresidual block from the bitstream received from the video encodingapparatus 400, perform inverse quantization with respect to the squareresidual block at the inverse quantizer 620, perform inverse transformwith respect to the square residual block at inverse transformer 630 andthen perform inverse rearrangement with respective to the squareresidual block into rectangular residual block.

In other words, inverse rearranger 640 rearranges the square residualblock 1120 illustrated in FIG. 11 back into the rectangular residualblock 1110 in a reverse process to reconstruct the first row of thesquare residual block 1120 into the first residual block 1112 of therectangular residual block 1110, the second row of the square residualblock 1120 into the second residual block 1114 of the rectangularresidual block 1110, the third row of the square residual block 1120into the third residual block 1116 of the rectangular residual block1110, and the fourth row of the square residual block 1120 into thefourth residual block 1118 of the rectangular residual block 1110.

When the rectangular residual block 1110 is reconstructed by the inverserearranger 640, intra predictor 660 of video decoding apparatus 600 setsthe rectangular current block as an 8×2 sized rectangle in accordancewith the prediction direction, predicts the value of each pixel in therectangular current block by using adjacent pixels A˜H which werepreviously decoded and are in proximity with the current block in thecurrently vertical prediction direction, and then adder 650 adds therectangular prediction block to the rectangular residual block togenerate the rectangular current block 1010.

Likewise, from the reconstructed rectangular current block, i.e. the 8×8block for the intra_(—)8×8 prediction at its second row pixels a₁˜h₁,the reconstructive prediction is performed with respect to the third andfourth row pixels a₂˜h₃ by using the reconstructed pixels a₁˜h₁ as thepredictors therefor. Likewise, the fifth and sixth row pixels may bepredicted from the fourth row pixels. The same process may be applied toall of the rows enabling the entire pixels in the macroblock to bepredicted starting from the adjacent pixel with the closest proximity inthe prediction direction before being compressed/reconstructed.

Similar to the vertical prediction direction, pixel predictions in thehorizontal direction may be performed for the entire pixels startingfrom the most proximal adjacent pixel for theircompression/reconstruction.

FIG. 12 at a and b illustrates the Rate-Distortion curves according tothe conventional and presently disclosed methods, respectively.

Illustrated in FIG. 12 are test results of the compression performanceof an embodiment wherein the block is constructed into a rectangle and aprediction is performed with respect to each of the current block pixelvalues from the most proximal adjacent pixel. Detailed test conditionsare indicated in Table 1 with the result reflecting the respectivepaired video images compressed by using the intra frames alone.

TABLE 1 Experiments Sequence Resolution condition Foreman, News QCIFHigh profile Container (176 × 144) Intra(I frame) only Paris, TempeteCIF Intra16 × 16 only (352 × 288) QP(20, 24, 28, City, ICE 4CIF 32, 36,40) (704 × 576) CABAC Deblockking Filter off

A comparison in the rate-distortion curve or R-D curve was made betweentypical H.264 where the prediction is done with square blocks and thepresent embodiment where the prediction of the rectangular block isfollowed by encoding the rearranged squared block. In the experiment,since the deblocking filer used in typical H.264 would not functionproperly in the present embodiment due to its fixed configuration forthe rectangular blocks, such a filter was not used in either of the testmethods. Table 2 shows the results.

TABLE 2 PNSR Bit Rate Reduction (%) difference Size Sequence QP20 QP24QP28 QP32 QP36 QP40 (average) QCIF Foreman 1.92 1.96 2.47 3.01 4.23 4.090.08 News 2.41 2.91 3.86 4.14 4.07 5.36 0.11 Container 3.42 4.00 4.805.47 7.44 6.57 0.06 CIF Paris 1.91 2.19 2.28 3.11 3.79 5.45 0.12 Tempete1.36 1.37 1.44 1.57 2.45 3.50 0.03 4CIF City 3.56 3.28 3.91 5.01 6.9610.10 0.12 Ice 4.36 7.32 11.22 9.84 12.44 15.28 0.13

As specified in Table 2, when the rectangular block based method ofprediction, encoding and decoding is carried out in parallel with theconventional square counterpart, bit rate reductions can be observed invarious experimental video images. In addition, the compared R-D curvesof images of a container in FIG. 12 at a and ice at b show the visibleperformance improvement over the conventional H.264 method.

Although exemplary embodiments of the present disclosure have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the disclosure.Therefore, exemplary embodiments of the present disclosure have not beendescribed for limiting purposes. Accordingly, the scope of thedisclosure is not to be limited by the above embodiments but by theclaims and the equivalents thereof.

INDUSTRIAL APPLICABILITY

As described above, the present disclosure is applicable to videoencoding/decoding where the current block of the video is predicted fromthe adjacent blocks, and is able to predict the entire pixels of thecurrent block starting from closest one of the pixels in the predictiondirection in preparation of encoding/decoding the video, and thusprovides a highly useful method to raise the compression efficiency thatin turn ensures more efficient video encoding/decoding performance.

CROSS-REFERENCE TO RELATED APPLICATION

If applicable, this application claims priority under 35 U.S.C §119(a)on Patent Application No. 10-2008-0058779 filed in Korea on Jun. 23,2008, the entire content of which is hereby incorporated by reference.In addition, this non-provisional application claims priority incountries, other than U.S., with the same reason based on the KoreanPatent Application, the entire content of which is hereby incorporatedby reference.

1. An apparatus for encoding an input video comprising: an intrapredictor for predicting a rectangular current block by using one ormore adjacent pixels according to a predetermined prediction directionand generating a rectangular prediction block; a block rectangle-shaperfor generating the rectangular current block according to the predictiondirection from the input video; a subtractor for generating arectangular residual block by subtracting the rectangular predictionblock from the rectangular current block; a rearranger for rearrangingthe rectangular residual block into a square residual block; atransformer for transforming the square residual block into a frequencydomain; a quantizer for performing quantization with respect to thetransformed residual block; and an encoder for encoding the quantizedresidual block into a bitstream.
 2. The apparatus of claim 1, whereinthe rectangular current block, the rectangular prediction block, and therectangular residual block are sized L×M with L being unequal to M. 3.The apparatus of claim 2, wherein the values of L and M are determinedin accordance with the prediction direction.
 4. The apparatus of claim2, wherein the value of L is greater than the value of M if theprediction direction is vertical.
 5. The apparatus of claim 2, whereinthe value of L is smaller than the value of M if the predictiondirection is horizontal.
 6. The apparatus of claim 1, wherein the one ormore adjacent pixels are encoded prior to encoding the rectangularcurrent block and are in proximity to the rectangular current block inthe prediction direction.
 7. A method for encoding an input videocomprising: performing intra prediction for predicting a rectangularcurrent block by using one or more adjacent pixels according to apredetermined prediction direction and generating a rectangularprediction block; performing a rectangle-shaping with respect to a blockfor generating the rectangular shape of the current block from the inputvideo according to the prediction direction; subtracting the rectangularprediction block from the rectangular current block and generating arectangular residual block; rearranging the rectangular residual blockinto a square residual block; transforming the square residual blockinto a frequency domain; performing quantization with respect to thetransformed residual block; and encoding the quantized residual blockinto a bitstream.
 8. An apparatus for decoding a video comprising: adecoder for decoding a bitstream and extracting residual block; aninverse quantizer for performing an inverse quantization with respect tothe extracted residual block; an inverse transformer for performing aninverse transformation with respect to the inverse quantized residualblock into a time domain; an inverse rearranger for performing aninverse rearrangement with respect to the inverse transformed residualblock into a rectangular residual block according to a predeterminedprediction direction; an intra predictor for predicting a rectangularcurrent block by using one or more adjacent pixels according to theprediction direction and generating a rectangular prediction block; anadder for adding the rectangular residual block to the rectangularprediction block in order to generate the rectangular current block; anda reconstructor for reconstructing the video for output by using therectangular current block according to the prediction direction.
 9. Theapparatus of claim 8, wherein the rectangular current block, therectangular prediction block, and the rectangular residual block aresized L×M with L being unequal to M.
 10. The apparatus of claim 9,wherein the values of L and M are determined in accordance with theprediction direction.
 11. The apparatus of claim 9, wherein the value ofL is greater than the value of M if the prediction direction isvertical.
 12. The apparatus of claim 9, wherein the value of L issmaller than the value of M if the prediction direction is horizontal.13. The apparatus of claim 8, wherein the one or more adjacent pixelsare encoded prior to encoding the rectangular current block and are inproximity to the rectangular current block in the prediction direction.14. A method for decoding a video comprising: decoding a bitstream andextracting residual block; performing an inverse quantization withrespect to the extracted residual block; performing an inversetransformation with respect to the inverse quantized residual block intoa time domain; performing an inverse rearrangement with respect to theinverse transformed residual block into a rectangular residual blockaccording to a predetermined prediction direction; performing an intraprediction with respect to a rectangular current block by using one ormore adjacent pixels according to the prediction direction andgenerating a rectangular prediction block; adding the rectangularresidual block to the rectangular prediction block in order to generatethe rectangular current block; and reconstructing the video for outputby using the rectangular current block according to the predictiondirection.
 15. An apparatus for encoding a video through predicting eachpixel in a current block of the video by using one or more adjacentpixels, the adjacent pixels being encoded prior to encoding the currentblock with the closest proximity to the pixels respectively in apredetermined prediction direction, and the current block being sizedL×M with L being unequal to M.
 16. An apparatus for decoding a videothrough predicting each pixel in a current block of the video by usingone or more adjacent pixels, the adjacent pixels being encoded prior todecoding the current block with the closest proximity to the pixelsrespectively in a predetermined prediction direction, and the currentblock being sized L×M with L being unequal to M.